Selective radioreceiver



April 2, 1935. D. GRIMEs SELECTIVE RADIORECEIVER Filed Jan. 9, 1932 NNNPatented Apr. 2, 1935 PATENT QF'FIC'EV SELECTWE RADIORECEIVERDavidGrmes. Donxan Hills, S. I., N. Y., assignor to Radio CorporationjofAmerica, a corporation of Delaware Applicationoanuary 9, 1932, serialN.A ssa-m1 7. Claims.

My present invention relates to radio-receivers, and more particularlyto a method of and means for, securing a high degreey ofselectivity in aradio receiver.

Various devices are resorted to at the present time in order to securemaximum selectivity in a radio receiver. For example, in a receiveremploying multi-stage tuned radio frequency amplification it iscustomary to employ several tunable circuits in cascade prior to thedetector stage.

The variable` condensers of these stages are arranged for uni-control byusually employing a gang condenser. As is well known to those skilled inthe art, the use of a gang condenser requires careful matching of thecondenser units of the gang, as well as matching of the cascaded radiofrequency circuits. The prior art contains many examples of differentarrangements which have beenresorted to for accomplishing such matching.

However, the use of a plurality of cascaded tuned radio frequencycircuits, which circuits are carefully matchedas to tuning devices, doesnot necessarily result in a receiver of a high degree of selectivity. Itis a wellknown fact that there is a practical limit beyond which furthercascading of tuned circuits will result in additional selectivity onlyat excessive cost. Accordingly, the superheterodyne type of radioreceiver is often employed in place ofthe tuned radio frequencyreceiver. Itis well known that the superheterodyne receiver isinherently selective to a high degree.

Nevertheless, when it is desired to achieve unicontrol tuning of thelocal oscillator, radio frequency and frequency changing circuits, it isa well known fact that recourse must be vhad to devices which are oftentroublesome in use and embodiment in the receiver. In any case,

whether the receiver be ofthe superheterodyne or tuned radio frequencytype, it is necessary to employ a gang condenser and careful matching ofa plurality of high frequency stages.

Now, I have discovered a novel 4method of, and devised simple means for,operating a, radio receiver so that it possesses a relatively highdeadvantage is taken of the welljknown frequencyv selectivecharacteristic of a piezo-electric crystal in'securing theaforementipnedresults. Fln'ther- (Cl. Z50-40) more, my prent receiver tuning deviceutilizes a phenomenonrpeculiar to an especially designed; piezo-electriccrystal. That isto say, I have observed that a piezo-electric crystal ofvariable thickness has a variable frequency selection characteristic.

Accordingly, it may be stated that it is -oneof the main objects ofA mypresent inventiontopr vide a high frequency receiving system compris inga plurality of high frequency-'amplifier circuits, a single `variabletuning device being utilized in advance ofthe amplifier` device `forimparting to the receiver'suiiicient selectivity. necessary. to receivesignals transmitted through.. a predeten mined range of frequencies.

Another important'object of the present in-` vention is to provide in aradio receiver, embody. ing a plurality of radio.y frequency amplifierstages, a variable tuning device whichavoidsthe necessity for theutilization of gang'condenser` and matching ofcascaded circuits, thetuningh device essentially comprising a piezo-electric elef mentdesigned in such a manner that it may` adjusted to resonateat aplurality of different frequencies ina desired range of frequencies.

Another object of the presentv inventionisto provide a piezo-electricvdevice, particularly4 adapted for tuningresonant high frequencycircuitsto different frequenciesin a desired range :of f

high frequencies, the device comprising aV crystal.

having atleast one facethereof disposed at avpre determined pitch withrespect toits other face, and an adjustable electrode movablyassociatedwith said first face.

And still another object of-the-present invention is to provide a tuningmeansfor a radio re-` ceiver comprising a piezo-electric'lcrystal vof iconstantly varying thickness, and an electrodeiso` designed and arranged-with respect to one -of the-v faces ofthe crystal that displacement ofsaid electrode produces a corresponding, and pre*- determined,frequencychange in the tuning means.

Still other objects of the invention areto improve generally thesimplicity and efiiciency `of high frequency signalling systems, and toparticu-4 larly provide a tuning means for aradio receiver which is notonly selectiveandreliablein operation, but economically manufactured andassembled in the receiver.

Thenovel features whiclrI believe-"to be'clfiaracteristic of -myinvention aresetfortlr in par ticularity in the `appended claims,the-'invention'- itself,- however; as -to both .its organization .andmethod of operaticniwill Ybest Vbe `understood 1b?- reference to thefollowing description taken in connection with the drawing in which Ihave indicated diagrammatically one circuit arrangement whereby myinvention may be carried into eiect.

In the drawing,

Fig. l is a schematic side elevation of the tuning means embodying thepresent invention,

Fig. 2 is a front elevation of the device shown in Fig. l,

Fig. 3 diagrammatically shows a radio receiver embodying the presentinvention.

Referring now to the accompanying drawing wherein like referencecharacters designate the same elements in the different figures, thereis shown in Figs. 1 and 2 a tuning device constructed according to theprinciples ofthe present invention. The piezo-electric element i variesfromV the design of a normal crystal of uniform thickness 'in that oneof its faces 2 is inclined with respect to a-lower face 3. That is tosay, the crystal l, which for example, may be a quartz crystal, isproduced by treating the face 2 of a normal crystal of uniform'thickness in such a manner that a crystal of constantly varyingthickness is produced. Thus, the face? may be designed to have thedesired pitch with respect to theface S by a grinding operation.Obviously,

'the means employed for securing the tapered crystal is of noconsequence as ar as the characteristic of the crystal is concerned. Itis suffiu cient that a crystal of constantly varying thickness isproduced. Those skilled in the prior art are, of course, well acquaintedwith the method of producing a normal crystal of uniform thickness.

The face 3 of the crystal is allowed to rest on a vbottom plate il, thelatter functioning as the fixed. electrode of the crystal For the upperelectrode of the crystal there is utilized a mobile contacter 5,'thelatter preferably consisting of the same metallic material as the plateai. It will be noted that the contactor 5 is disposed in sliding contactwith the inclined crystal face 2, and that `Figs. l and 2 as a frequencyselector.

it comprises in fact a thin strip of metal having a'length greater thanthe breadth of the crystal 2.

The contacter 5 may be arranged for sliding movement over the crystalface 2 by securing it to a moving rack 6. The securing means between theelectrode 5 and the rack E may comprise any means well known to thoseskilled in the art, as for example three metallic, rigid members Amanipulating knob 8 provided with a shaft 9 and pinion it may beemployed for driving the rack t. It is to be understood, however, thatany other desired driving means may be employed for adjusting theposition of the mobile electrode 5. with respect to the crystal face 2.

When the device shown in Fig. 1 is employed asaftuning means for aresonant circuit, the end of the crystal l which has the minimumthickness comprises the high frequency end of the tuning device, whilethe opposite end, that of maximum thickness, constitutes the lowfrequency end of the tuner.

-InFig 3 there is schematically shown a signalling system, such as aradio receiver, which is ,arranged for utilizing the device shown inThus, the receiver comprises a source of signal energy S which iscoupled, as at M,- to the resonant input circuit of a stage of radiofrequency amplification conventionally represented. The signal en-`rergy source 'is preferably the usual antenna circuit for collectingsignal energy of all frequenamplifier.

cies, or it may even comprise a preceding stage: of untuned radiofrequency amplification coupled. to a prior antenna system foramplifying thecol-A lected signal energy prior to frequency selection;

in the tuned stage. The tuned stage comprises the inductance coil L andthe piezo-electricv tuning device arranged in shunt therewith.

There is inserted a high ohmic resistance R (preferably around 500,000ohms) between` coil L and the crystal in Fig. 3. This is necessary toenable the crystal to tune in the desired signal and reject'theundesired ones. In such a circuit the crystal itself .is acting as acomplete tuned anti-resonance circuit such as we have when using a coilVand condenser. The resistance R has a neglible eiiect at the resonancefrequency of vthe crystal so that the entire voltage of coil L isavailable tov the input grid of the succeeding However, off resonance,the impedance of `the crystal drops and the voltage of the coil L isgreatlyreduced by the resistance R so that the olf-resonance ,signalshave no appreciable magnitude when they reach the grid of the amplifier.

The tuning device is shown in a simplified manner, the tapered crystal lbeing shown mounted upon the bottom electrode 4, the arrow 5'corresponding to the adjustable contacter 5. A'lead il connects thebottom electroder 4 to the low potential side of the coil L. Thepiezo-electric tuner `is arranged in the input circuit of a radioamplification stage, as pointed out above, and it is to be understoodthat the amplier may comprise any type of electron discharge tube wellknown to those skilled in the art, the ampliiied output of the amplierbeing impressed as at M1, upon the input circuit of a multi-stageuntuned radio frequency amplifier. Of course, a single untuned radiostage can follow the tuned radio amplifier if desired.

Any well known type of detector circuit may have its input coupled, asat M2 to the output of the untuned radio amplifier, the detected outputbeing impressed upon the input, as at M3, of an audio -frequencyamplifier. The latter may comprise'one or more stages of amplincation.Any well known type of utilization means may be coupled to the output ofthe audio amplifier, and such Vutilization means may comprise a loud-lspeaker, head phones or any other desired type ofreproducing means forelectrically transmitted intelligence. For a reason to be described in,further detail at a later point, the audio ampli` fier is preferablygiven a rising frequency characteristic. That is to say, a compensatingaudio amplifier is employed, the amplifier transmitting the higher audiofrequencies to a greater extent than the lower audio frequencies.

Considering, now, the operation of the signal ling system shown in Fig.3, and particularly the functioning ofthe tuning device disclosedtherein, it is pointed out that it is merely necessary to move theelectrode 5' of the inclined face 2 of the piezo-electric crystal inorder to vary the frequency setting of the receiver. As stated above,the present tuning device applies a phenomenon observed inpiezo-electric devices.

The phenomenon, without entering into detailed cies throughout apredetermined rangeV of frequencies, as an electrode, comprising anarrow strip compared to the bottom electrode, is moved along theinclined face of the crystal, and in sliding contact therewith.

In other words, after calibration of the tuning device, a definiteposition of the electrode along the face 2 corresponds to apredetermined frequency. It is suflicient to point out at this time thatthe frequency at which a pieno-electric crystal resonates is inverselyrelated to the thickness of the crystal, it being understood of coursethat the crystal portion whose thickness is under consideration isdisposed between a pair of electrodes. Thus, it will be seen that moving.the electrode 5 towards the thicker end of the crystal I results lnresonating the crystal to a relatively low frequency compared with thefrequency to which the less thicker portions of the crystal areresonant.

It will now be realized that adjustment of the electrode 5' in Fig. 3results in frequency selection, since only electrical energy of afrequency corresponding to the frequency setting of the member 5' willbe transmitted between the source S and the rst stage of radio frequencyamplification. It is well known to those skilled in the art that apiezo-electric crystal coupling circuit between a source of signalenergy of a group of frequencies and a radio amplifier will transmitonly such energy which has a frequency substantially equal to thefrequency of the coupling circuit. That is to say, the single tunedstage in Fig. 3 is sharply selective, and as a matter of fact would beso selective as to give all the selectivity necessary in a radioreceiver.

Furthermore, the tuned stage is a variable one, and hence avoidsmatching of any tuning devices and cascaded circuits, since thesucceeding amplifier stage, or stages, are untuned. It is obvious thatthe crystal I, and its electrodes l and 5, as well as the motion of themanipulating knob 8 may be so designed that frequency selection throughany predetermined range of frequencies may be effected.

To compensate for the sharp cut-off characteristic of the piezo-electriccrystal I at the higher side band frequencies, a compensating audiofrequency amplifier may be employed. The latter may be employed in orderto preserve ildelity since the crystal tuning device is sharplyselective and tends to produce a sharp, peaked resonance curve. That isto say, the upper side band frequencies on each side of the acceptedcarrier are transmitted through the crystal with less efficiency thanthe lower side band frequencies. Hence, by employing an audio amplifierwhich has a rising frequency characteristic, that is one which amplifiesthe higher audio frequencies to a greater extent than the lower audiofrequencies, the sharp cut-olf characteristic of the piezo-electrictuner is compensated for.

While I have indicated and described one arrangement, for carrying myinvention into effect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention as set forth in the appendedclaims.

What I claim is:

l. A tuning device comprising a piezo-electric crystal of varyingthickness, an electrode affixed to a face thereof, and a secondelectrode in contact with another face of the crystal, and means foradjusting the position of the second electrode with respect to saidsecond face by displacing the second electrode along different elementalareas of the face of the crystal.

2. A tuning device comprising a piezo-electric crystal of constantlyvarying thickness, an electrode alxed to a face thereof, and a secondelectrode in contact with another face of the crystal, and means foradjusting the position of the second electrode with respect to saidsecond face by displacing the second electrode along different elementalareas of the face of the crystal.

3. A tuning device comprising a tapered piezoelectric crystal, anelectrode afllxed to a face thereof, and a second electrode in contactwith another face of the crystal, and means for adjusting the positionof the second electrode with respect to said second face by displacingthe second electrode along different elemental areas of the face of thecrystal. v

4. In combination, a piezo-electric crystal having one face thereofdisposed at an incline with respect to another face, a metallicelectrode adjacent to the non-inclined face, and an adjustableelectrode, comprising a narrow metallic strip, in sliding contact withsaid inclined face.

5. In a signalling system including an electronic tube provided withoutput terminals and input terminals, an input circuit for said tubeincluding a piezo-electric crystal connected across the input electrodesof the tube and a high impedance element, Said crystal having one facethereof inclined with respect to another face, a metallic electrodeadjacent to the non-inclined face and an adjustable electrode comprisinga narrow metallic strip in sliding contact with the inclined face, saidtwo electrodes being arranged so as to connect the crystal across saidinput terminals.

6. In combination a piezo-electric crystal having one face thereofdisposed at an incline with respect to another face thereof, anelectrode adjacent to one of said faces and an adjustable electrode inthe form of a narrow strip as compared with the crystal in slidingcontact with said inclined face and means for varying the position ofthe adjustable electrode along the inclined face of the crystal.

7. In a signalling system including an electronic tube provided withoutput and input electrodes, an input circuit for said tube including apiezoelectric crystal connected across the input electrodes of the tubesaid crystal having one face thereof ground at an angle with respect tothe opposite face thereof, electrodes for each of the said two crystalfaces for connecting the crystal in said input circuit, means foradjusting one of said electrodes with respect to its associated crystalface by displacing the last named electrode along different elementalareas of the associated face of the crystal to thereby tune the inputcircuit of the tube.

DAVID GRIMES.

Cil

